Heterogeneous integration of 8-inch LiNbO3 films for second harmonic generation

Abstract

Lithium niobate (LiNbO₃, LN), known for its exceptional piezoelectric, electro-optic, and nonlinear optical properties, holds significant promise for applications in microelectronics, optoelectronics, and integrated photonics. However, the direct epitaxial growth of LN on Si substrates remains a formidable challenge due to the substantial lattice mismatch and thermal expansion coefficient disparity between LN and Si. In this work, an 8-inch LN-on-SiO₂ hetero-integrated wafer was successfully fabricated using plasma-activated bonding (PAB) technology, with a PECVD-deposited SiO₂ film serving as the intermediate layer. During the bonding process, the amorphous SiO₂ film at the hetero-interface underwent recrystallization, achieving a recrystallized thickness of approximately 3.4 nm. The mechanical robustness of the bonding interface was evaluated via shear force tests on 2 × 2 mm samples, revealing that the fracture path propagated into the bulk of the sample rather than remaining confined to the bonding interface. This finding indicates that the bonding interface strength is comparable to that of the sample bulk. Furthermore, second harmonic generation (SHG) measurements demonstrated a strong linear relationship between SHG peak intensity and excitation power, with a slope of 2.03, thereby confirming the superior nonlinear optical performance of the hetero-integrated LN film. This study not only advances the understanding of the nonlinear optical properties of hetero-integrated LN films but also paves the way for broader applications of LN materials across diverse fields.